Radio navigation system and method



Dec. 30, 1947. H. G. BusxGNlEs RADIO NAVIGATION SYSTM AND METHOD FiledMay l, 1944 3 Sheets-lSheec l IN VEN TOR. 'MEN/el r-i. 5ms/ames ATTOR/VEY Dec. 30, 1947. H. G. BusxGNlEs 2,433,341

RADIO NAVIGATION SYSTEM AND METHOD Filed May l, 1944 3 Sheets-Sheet 2/Yf v y v JJ y 1521i la 15H/ la la le Hz//Z .n

TIME

Dec. 30, 1947. H. G. BuslGNu-:s

` RADIO NAVIGATION SYSTEM ANDl METHOD Filed May l, 1944 5 Sheets-Sheet 3lIN VEN TOR. HENR/ G. I/.S//Y/E'S BY Y NSS

ATTORNEY Patented Dec. 30, u,1947

RADIO NAVIGATION SYSTEM AND METHOD Henri G. Busignies, Forest Hills, N.Y., assignor to Federal Telephoneand Radio Corporation, New York, N. Y.,a corporation of Delaware Application May 1, 1944, Serial No. 533,465

Claims.

This invention relates to radio navigation systems and more particularlyto radio distance and direction indicating systems suitable forsimultaneous use by a plurality of aircraft.

Systems for controlling aircraft navigation have been proposed whereinthe position of a craft relative to one or more fixed locations isobtained by the timing of pulses transmitted from the craft to the xedlocations and received again on the craft after repeating -at the xedlocations. However, in these previously proposed systems a high degreeof stability in the pulse recurrence frequency is required. Furthermore,these proposed systems are not well adapted for simultaneous use by aplurality of different aircraft.

It is a principal object of my invention to provide a simple radiodistance indicating system and method suitable for navigation.

It is a further object of my invention to provide a simple system andmethod by which each of a plurality of aircraft may determine theirdistances from one or more fixed locations and simultaneously obtain adirectional reading with respect to said stations.

It is a still further object of my invention to provide a navigationequipment which requires on the craft very little additional indicatingapparatus.

According to a feature of my invention, kl provide on an aircraft,pulsing equipment for transmitting relatively widely spaced pulses onthe same radio frequency carrier. These pulses from each of thecraft arereceived on a single repeater apparatus which serves to repeat thepulses in the same order in which they are received. The pulses arereceived back on the various craft and are applied to an indicator, forexample, a cathode ray type indicator to indicate the distance of thecraft from the repeater station. 1n order that each craft may receiveits own indication to the exclusion of those pulses repeated from theother craft, the trains of pulses transmitted from each craft are givena different recurrence frequency characteristic. For example, therecurrence or repetition frequency of the pulses may be wobbled atdifferent xed or random rates on the different craft so that theynormally will not coincide, or diiferent repetition frequencies may beused by each craft. The distance indicator on each craft will betriggered to provide a reference point depending upon each transmittedpulse. Consequently, the pulses received from the other craft `withdilferent timings will not cumulatively effect the indicator and will beeasily distinguished from the desired distance indications. On the whichserves to energize pulse generator 2.

aircraft, the normal communication transmitter craft receiver may beprovided with a directive antenna so that a directional indication maybe obtained at the same time that the distance indication is being made.Thus, a craft may be able to ascertain its distance and direction withrespect to a single station so that its position Will be accuratelydeiined. Alternatively or in conjunction with the direction and distanceindication, measurements may be made from two or more spaced repeaterstations so that the position of the craft may be checked by atriangulation method.

A better understanding of my invention and the objects and featuresthereof may be had from the particular description of an embodiment madewith reference to the accompanying drawings in which:

Fig. 1 is a block circuit diagram illustrating the relationshipv of thecraft equipment and the repeater station;

Fig. 2 is a set of curves used in explaining the operation of myinvention;

Fig. 3 is a further set of curves on a larger scale illustrating thedistance finding principles of my invention; and v Fig. 4 is afragmentary view of a cathode ray oscilloscope screenshowing how thedistance indications are separately cumulatively indicated.

Turning rst to Fig. l, the aircraft equipment may comprise a wobbledfrequency generator I, The pulses from pulse generator 2 are applied totransmitter 3 so that radio frequency pulses are transmitted fromantenna 4. These radio frequency pulses are received on antenna 5 andapplied to a receiver 6. The output pulses from receiver 6 serve totrigger a transmitter 1 which radiates from antenna pulses correspondingto those received on the receiving antenna 5. Preferably the receiver Eis blocked by the received signals in any known manner for a shortperiod while pulses are being transmitted in order to avoid signaling.Pulse energy from .antenna 8 is re' ceived on antenna 9 which may be arotatable directional receiving antenna, as shown. Although a singleloop antenna'is illustrated, any other known type of directional antennaor' array may be used. These received pulses are applied to receiverdetector' Ill which serves to produce output pulses of the envelope ofthe pulse trains received'on antenna 9. In order to prevent thetransmitter directly aiecting the receiver, a blocking circuit Il to theoutput of pulse genera'- tor 2, serves to block receiver detectorIllduring the periods of transmission from antenna d.

The detected pulses in the receiverl l0 are applied to a control grid l2of a `cathode ray oscil'- loscope I3. Grid l2 is preferably biased sothat in the absence of pulses applied from receiver l0, the intensity oflcathode ray beam will be reduced. For the operation of the oscilloscopeto determine distance,.energy from vrpulse generator 2 is applied to a:time base generator |31 which serves to apply a time base potential todeection coils I5, I6. Deilection coils I5 and I6 are arr-- ranged forrotation about the cathode ray .oscilloscope I3 simultaneously-withrotation off-:antenna 9, as indicated by broken lines ISI. As aconsequence, the cathode ray 'beamgis Adeilected radially across thescreen of .the .oscilloscope t.by potential applied to coils I5, I6, andis Vrotated angularly about the screen with rthe rotating fdirectiveantenna. Thus, in response to fenergyreceived on antenna 9, aspot orseries of spots of light will be .made to appear, as shown at I9. Thisspot will appear radially ldisplaiced'from the center in accordance withthe distance of the craft from the single repeaterstation, and willbeVan-gularly displaced in accordance Awith the directional antennai9.`The distance ofthe craft from the repeaterwill be indicated by thisvradial displacement on the 'distance scale indicated by lthe concentric'circles I8. lOther repeated pulses .and directly transmittedpulses'irom the other craft, received on antenna'9 will 'occurat dier-4ent timing intervals corresponding Vto different distance indications,as shown by the spots 29,'2I cutlinedjin -light A"lines on Athe"oscilloscope screen. In fact, since rthe wobbled Vor recurrence ratevc'zhangesf-rom the various'craftareoompletely unsynchronizedwithrespect to anyfother craft,-'these spots such as 20, 2|, mayappearonly a'single time-in one Aposition and Awill V'not producereadable lindications on -thesCreen.

Other craft, as shown at 22, are'equipped with their own distanceanddirectionindication equipment similar to that speci'callydescribedabove, andare provided with `transmittingantennas 23 and receivingantennas 2d. A plurality of such craft may simultaneously transmitApulses at diff.

ferentrepetition-rates, tothe repeater station and each will produce`its own Yindications vas fdistinguis'hed :from those' ofother crafts.

vThe use :of =the directional antenna with the Ipulse repeater systemserves to provide sharper `directional indication free l'fromreflectionerrors than-wouldbebtained:forlong continued waves. Any pulse,reaching antenna "-9, after reection lfrom other obstacles, will appear'at a different apoint on the distance `scale from vthe pulses directlytransmittedlto the receiver without reflecition. lAnypulse receivedafter ireilec'tion will arrive. at Va later time :and `will vgive .theyappearance fof coming from a greater distance vthan the diuectlyreceived ypulse, Aso that the-indicationof the :shortest :distance willusua'llybe the pulse to read for ydirection :finding .purp'oses.Furthermore, the reected vpulses are vmuch weaker and will -not zshow11p as brightly as -does lthe ldirectly received pulse indication.

:Ets'houldbe understood that for direction'iindina-the antennas such Ias"e lor 2Q are rotated relaitively Aslowly with respect to the pulserepetition metes-'s0 that the ypulses `have ampletime 'to trav- @rse thedistance from (the. craft to 'the repeater @mi back abeforeanyappreciable change 'in the nngularfnosition of;.the-frotaryadirectionalantenna AQQQIZIITS.

Beierrins to Fig. f2, an explanation .of the .m an nerinfwhich thepulsesfrom different craft may .be azariablyl transmitted lat `variablerepetition fratesuisexplained. Gurves'fZ'a, ZboiFig. '2,-showr`1 M2525,:25, may 'represent two 'waves produced by ilierent craft in vdiierentwobbled frequency 3generater's such as generator I -of Fig., Reeticationof these Waves produces the curves .shown Y.at `2c, 2d, indicated byreference ccharaciters i251: .and26d, respectively. F'These rectifiedwaves may be clipped at the respective clipping levels 21 and 28 toproduce resultant pulses, as shown in curves 2e, 2f. In curve 2e, theresultant pulses from :curvel25c are shown at 29, and at 30 Vvare shown.the retransmitted received pulses on the .corresponding `[indicatorreceiver. In curve 2j, pulsesI-represent the resultant pulses from curve26d and pulses 32' represent the retransv,mitted pulses from this serieswhich may be received vatthe same indicator as received pulses 30. Thecomposite Wave received on the receiver at the single repeater stationis indicated by curve 2g. 'It will be observed-that the-pulses 29 and 3|are here related to one )another "in a 4random manner.

A clearer understanding of the 'operation of the indicators may be hadbyreference to Fig. 3 showing on agreatly exaggerated scale the relationof two craft systems to one-another. In this ligure curves 3a, 3b, showon'an enlarged scale the time "relationship of the transmitted pulses29, l3| Aat `the'repeater -and the repeated pulses 30, 32 at a -singlecraft. 'It will be `noted that the spacing to travel `from thel'singlerepealter to lany single receiver will'be the Ysame regardlessof vwhere the pulses which trigger the-repeater'come from. If -We assumefirst, an indicator located 'on Va lcraft which produces'the series oflpulses V29, the sweep of l-thisindicator Imaybe represented, forexample, lbythe Vsaw-tooth wave l33 of curve'3c. On this Asaw-tootlnwave Ypulses A43|) 4occur wat a fixed distance ffrom the yorigin o'f thesweep in every'case, :while :pulses 3|Cand -32 representing lthedirectly received pulses, and the corresponding received retransmittedpulses, respectivelyfappear at various .spaced points Aalong this curve.Pulse SIC :will `generally diier -from 'the position shown in curve 3bbecause of the difiering distance between craft. At-one position incurve "3c pulses 39 and v32"-ccinc'ide. However. -the occasionalycoincidence Awill not adversely effect the reading on the `indicators.In curve 3d,-is shown a saW-'toothwave :3A similar :to wave 33representing vthe indicator vsweep on the craft at Which-pulses'SIoriginate. Here it willlbe noted,pulses32 occur at relatively 1iixed.positions on the 'saw-'tooth waves 3'4, while :pulses .29d and '39 arevariably displaced.

In lFig. 4 is shown the screen of la simpleform of ,cathode vray`distance indicator in which the sweep 34" is made in a rectilinear`fashion'under 'the 'control of a saw-tooth wave, 'such fas shown.-at33. lAssuming that-'this is :the sweep according 'to vthe wavevcurve 3c the indications V39a corresponding to pulses 30 yall occur ata relatively .flxeddistance alongthe sweep. Thus, a cumulative efectisproduced making' pulses 30a stand 'out brightly. However, pulses 32a,corresponding 'to' the variable-position of repeated pulses '32, andy.pulses IC representing directly-received pulses3 I, are `spread :out:along the 'scale'y and, 4as -a consequence, willbe -ve-rymuc'h dimmer'than vwill be the indication 39a. A

vWhile'I have. described va s'pecicenibodi-ment'- of vmy invention finwhich the `pulses transmitted fromv separate receivers Vare transmittedat variaf- 'ble `repetition rates under' control of" a wobbled frequencygenerator, it should beunders'tood that this Vfeature is not-necessaryto the operation o'f the invention. If the transmitters on each ,of thecraft operate at different fixed repetition rates,

the timing circuits will still segregate to a large extent the wantedpulses from the unwanted pulses and thus will produce the desiredindication. Such a circuit may be represented merely by omitting thewobbled frequency generator illustrated inFig. 1. 4

It should be further understood that the separate pulse generators neednot be controlled in synchronism but may be permitted to operate atrelatively random pulsing rates. In such a system the occurrence ofsimultaneous reception of pulses at the repeater will likewise berelatively small. It should further be understood that desired separatedirection and distance indicators may be provided instead of thecombined direction and indicating arrangement illustrated. Many othermodifications of my invention will readily occur to those skilled in theart. Accordingly, the description of the specific embodiment andmodifications thereof is not intended as a limitation on my invention,as set forth in the objects of my invention.

What is claimed is:

1. In a system in Which a plurality of craft may each simultaneouslyobtain indications f its distance from a single station by repetition ofpulse trains, a method of distinguishing the respective indications ateach craft from indications produced by the repeated pulse trains fromother craft, comprising transmitting individual pulse trains from eachcraft, giving to the pulses of said ltrains distinctive characteristicrepetition rates including varying such repetition rates, receiving andretransmitting all said pulse trains at said single station, receivingretransmitted pulse trains on each of said craft, and producingidentication of each of said craft timed with respect to the separatepulses of the train of pulses transmitted from each of said craft,whereby the repeated pulses from the pulse train transmitted from eachcraft produce cumulative indications on the corresponding craft Vwhichdistinguish from the received pulses of other craft.

2. In a system in which a plurality of craft may each simultaneouslyobtain indications of its distance from a single station by repetitionof pulse trains, a method of distinguishing the respective indicationsat each craft from indications produced by the repeated pulse trainsfrom other craft, comprising transmitting individual pulse trains fromeach craft, giving to the pulses of said trains distinctivecharacteristic repetition rates including varying the timing of saidpulses at randomly related variable repetition rates, receiving andretransmitting all said pulse trains at said single station, receivingsaid retransmitted pulse trains on each of said craft, and producing anindication on each of said craft timed with respect to the separatepulses of the train of pulses transmitted from each of said craft,whereby the repeated pulses from the pulse train retransmitted from eachcraft produce cumulative indications on the corresponding craft whichdistinguish from the received pulses of other craft.

3. In a system in which a plurality of craft may each simultaneouslyobtain indications of its distance from a single station by repetitionof pulse trains, a method of distinguishing the respective indicationsat each craft from indications produced by the repeated pulse trainsfrom other craft, comprising transmitting individual pulse trains fromeach craft, giving to the pulses of' said trains distinctivecharacteristic repetition rates including varying the timing of saidpulses at different repetition rates, receiving and retransmitting allsaid pulse trains at said single station, receiving said retransmittedpulse trains on each of said craft, and producing an indication on eachof said craft timed with respect to the separate pulses of the'train ofpulses transmitted from each of said craft, whereby the repeated pulsesfrom the pulse train transmitted from each craft produce cumulativeindications on the corresponding craft which distinguish from thereceived pulses of other craft.

4. A system for obtaining simultaneously, on each of a plurality ofcraft, indications of its distance from a single station by means ofrepeated pulses on a common radio frequency. comprising means fortransmitting from each craft trains of pulses, control means for givingto the pulses of each train randomly related variable repetition rates,means at said single station for receiving the pulses from all saidtrains and repeating them at substantially the same repetition rates atwhich they are received, means on each of said craft for receiving saidrepeated pulses, indicator means on each of said craft, timing meansresponsive to the pulses transmitted from each of said craft forproviding a time reference scale on said indicator, means for applyingsaid received pulses to said indicator, whereby said indicator undercontrol of said timing means will provide a cumulative indication of therepeated pulses corresponding to the respective transmitted pulse train.

5. A system for obtaining simultaneously, on each of the plurality ofcraft, indications of its distance from a signal station by means ofrepeated pulses on a common radio frequency, com-. Vprising means fortransmitting from each craft trains of pulses, control means for givingto the pulses of each train dierently, variably timed repetition rates,means at said single station for receiving the pulses from all saidtrains and repeating them at substantially the same repetition rates atwhich they are received, means on each said craft for receiving saidrepeated pulses, indicator means on each of said craft, timing meansresponsive to the pulses transmitted from each of said craft forproviding a time reference scale on said indicator, and means forsupplying said received pulses to said indicator, whereby said indicatorunder control of said timing means will provide a cumulative indicationof the repeated pulses corresponding to the respective transmitted pulsetrain.

HENRI G. BUSIGNIES.

REFERENCES CITED The following references are of record in the file ofthis patent:

'UNITED STATES PATENTS Number Name Date 2,143,035 Smith Jan. 10, 19392,134,716 Gunn Nov. 1, 1938 2,248,215 Budenbom July 8, 1941 2,252,083Luck Aug. 12, 1941 FOREIGN PATENTS Number Country Date Y `520,778 GreatBritain May 3, 1940

